At Opera, we have been building web browsers for more than 20 years. We are very aware that some parts of the web browsers we know today are nothing more than tributes to the last millennium – a time when the web was mostly made up of documents and pages._________________Hiromichi

At Opera, we have been building web browsers for more than 20 years. We are very aware that some parts of the web browsers we know today are nothing more than tributes to the last millennium – a time when the web was mostly made up of documents and pages.

I suppose you could substitute "achievements of" but really, it's the idea that current web browsers are using some older technology that was used in the last millennium.